Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power). Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency divisional multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.
These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of an emerging telecommunication standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). It is designed to better support mobile broadband Internet access by improving spectral efficiency, lower costs, improve services, make use of new spectrum, and better integrate with other open standards using OFDMA on the downlink (DL), SC-FDMA on the uplink (UL), and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.
User equipment (UE) employ these technologies to communicate with evolved Node Bs (eNB) to access core network components and functionalities. In one example, UEs can communicate to eNBs using LTE in an unlicensed or shared frequency spectrum (LTE-U). In some cases, the utilized spectrum may include frequencies used in other types of networks, such as wireless local area networks (WLAN) employing Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi). These networks can implement listen-before-talk (LBT) mechanisms where devices perform a clear channel assessment (CCA) to acquire or gain access to a channel and can communicate over the acquired channel without requiring scheduling of resources. Where LTE is employed over these networks, transmitting hybrid automatic repeat/request (HARQ) feedback may not comply with current LTE standards based on scheduled grants as a UE may not be able to acquire a channel (e.g., perform a successful CCA) at the time when the feedback is due according to the LTE standards. In addition, executing the CCA for transmitting each feedback transmission may be burdensome to network resources and may cause additional delay in transmitting the feedback.